the cellular environment: fluids and electrolytes, acids and bases chapter 3 mosby items and derived...

The Cellular Environment: Fluids The Cellular Environment: Fluids and Electrolytes, Acids and Basesand Electrolytes, Acids and Bases

Chapter 3Chapter 3

Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.

2Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.Mosby items and derived items © 2010, 2006 by Mosby, Inc., an affiliate of Elsevier Inc.

Distribution of Body FluidsDistribution of Body Fluids Total body water (TBW)Total body water (TBW)

Intracellular fluidIntracellular fluid Extracellular fluidExtracellular fluid

• Interstitial fluidInterstitial fluid

• Intravascular fluidIntravascular fluid

• Lymph, synovial, intestinal, biliary, hepatic, pancreatic, Lymph, synovial, intestinal, biliary, hepatic, pancreatic, CSF, sweat, urine, pleural, peritoneal, pericardial, and CSF, sweat, urine, pleural, peritoneal, pericardial, and intraocular fluidsintraocular fluids


Water Movement Between Water Movement Between the ICF and ECFthe ICF and ECF

Osmolality Osmolality Osmotic forcesOsmotic forces AquaporinsAquaporins Starling hypothesisStarling hypothesis

Net filtration = forces favoring filtration – forces Net filtration = forces favoring filtration – forces opposing filtrationopposing filtration


Water Movement Between Water Movement Between the ICF and ECFthe ICF and ECF


Net FiltrationNet Filtration Forces favoring filtration Forces favoring filtration

Capillary hydrostatic pressure (blood pressure)Capillary hydrostatic pressure (blood pressure) Interstitial oncotic pressure (water-pulling) Interstitial oncotic pressure (water-pulling)

Forces favoring reabsorptionForces favoring reabsorption Plasma oncotic pressure (water-pulling)Plasma oncotic pressure (water-pulling) Interstitial hydrostatic pressureInterstitial hydrostatic pressure


Osmotic EquilibriumOsmotic Equilibrium


Alterations in Water Movement: Alterations in Water Movement: EdemaEdema

Accumulation of fluid within the interstitial Accumulation of fluid within the interstitial spacesspaces

CausesCauses Increase in capillary hydrostatic pressureIncrease in capillary hydrostatic pressure Losses or diminished production of plasma albuminLosses or diminished production of plasma albumin Increases in capillary permeabilityIncreases in capillary permeability Lymph obstruction (lymphedema)Lymph obstruction (lymphedema)


Water BalanceWater Balance

Thirst perceptionThirst perception Osmolality receptorsOsmolality receptors

• Hyperosmolality Hyperosmolality

Baroreceptors stimulatedBaroreceptors stimulated• Plasma volume depletionPlasma volume depletion

ADH secretionADH secretion


NaNa+ + and Cland Cl–– Balance Balance

SodiumSodium Primary ECF cationPrimary ECF cation Regulates osmotic forcesRegulates osmotic forces RolesRoles

• Neuromuscular irritability, acid-base balance, and cellular Neuromuscular irritability, acid-base balance, and cellular reactionsreactions

ChlorideChloride Primary ECF anionPrimary ECF anion Provides electroneutralityProvides electroneutrality


NaNa+ + and Cland Cl–– Balance Balance

Renin-angiotensin-aldosterone systemRenin-angiotensin-aldosterone system AldosteroneAldosterone

Natriuretic peptidesNatriuretic peptides Atrial natriuretic peptideAtrial natriuretic peptide Brain natriuretic peptideBrain natriuretic peptide Urodilantin (kidney)Urodilantin (kidney)


Alterations in NaAlterations in Na++, Cl, Cl––, and Water , and Water BalanceBalance

Isotonic alterationsIsotonic alterations Total body water change with proportional Total body water change with proportional

electrolyte changeelectrolyte change Isotonic volume depletionIsotonic volume depletion Isotonic volume excessIsotonic volume excess


Hypertonic AlterationsHypertonic Alterations

HypernatremiaHypernatremia Serum sodium >147 mEq/LSerum sodium >147 mEq/L Related to sodium gain or water lossRelated to sodium gain or water loss Water movement from the ICF to the ECFWater movement from the ICF to the ECF

• Intracellular dehydrationIntracellular dehydration

Manifestations: intracellular dehydration, Manifestations: intracellular dehydration, convulsions, pulmonary edema, hypotension, convulsions, pulmonary edema, hypotension, tachycardiatachycardia



Water deficitWater deficit DehydrationDehydration Pure water deficitsPure water deficits Renal free water clearanceRenal free water clearance ManifestationsManifestations

• Tachycardia, weak pulse, and postural hypotensionTachycardia, weak pulse, and postural hypotension

• Elevated hematocrit and serum sodium levelsElevated hematocrit and serum sodium levels



HyperchloremiaHyperchloremia Occurs with hypernatremia or a bicarbonate deficit Occurs with hypernatremia or a bicarbonate deficit Usually secondary to pathophysiologic processesUsually secondary to pathophysiologic processes Managed by treating underlying disordersManaged by treating underlying disorders


Hypotonic AlterationsHypotonic Alterations

Decreased osmolalityDecreased osmolality Hyponatremia or free water excessHyponatremia or free water excess Hyponatremia decreases the ECF osmotic Hyponatremia decreases the ECF osmotic

pressure, and water moves into the cell pressure, and water moves into the cell Water movement causes symptoms related to Water movement causes symptoms related to

hypovolemiahypovolemia


Hypotonic AlterationsHypotonic Alterations

HyponatremiaHyponatremia Serum sodium level <135 mEq/LSerum sodium level <135 mEq/L Sodium deficits cause plasma hypoosmolality and Sodium deficits cause plasma hypoosmolality and

cellular swellingcellular swelling• Pure sodium deficitsPure sodium deficits• Low intakeLow intake• Dilutional hyponatremiaDilutional hyponatremia• Hypoosmolar hyponatremiaHypoosmolar hyponatremia• Hypertonic hyponatremiaHypertonic hyponatremia


Hypotonic AlterationsHypotonic Alterations Water excessWater excess

Compulsive water drinkingCompulsive water drinking Decreased urine formationDecreased urine formation Syndrome of inappropriate ADH (SIADH)Syndrome of inappropriate ADH (SIADH)

• ADH secretion in the absence of hypovolemia or ADH secretion in the absence of hypovolemia or hyperosmolalityhyperosmolality

• Hyponatremia with hypervolemiaHyponatremia with hypervolemia

Manifestations: cerebral edema, muscle twitching, Manifestations: cerebral edema, muscle twitching, headache, and weight gainheadache, and weight gain


Hypotonic AlterationsHypotonic Alterations HypochloremiaHypochloremia

Usually the result of hyponatremia or elevated Usually the result of hyponatremia or elevated bicarbonate concentrationbicarbonate concentration

Develops due to vomiting and the loss of HClDevelops due to vomiting and the loss of HCl Occurs in cystic fibrosisOccurs in cystic fibrosis


PotassiumPotassium Major intracellular cationMajor intracellular cation Concentration maintained by the NaConcentration maintained by the Na++,K,K++ pump pump Regulates intracellular electrical neutrality in Regulates intracellular electrical neutrality in

relation to Narelation to Na++ and H and H++

Essential for transmission and conduction of Essential for transmission and conduction of nerve impulses, normal cardiac rhythms, and nerve impulses, normal cardiac rhythms, and skeletal and smooth muscle contractionskeletal and smooth muscle contraction


Potassium LevelsPotassium Levels Changes in pH affect KChanges in pH affect K++ balance balance

Hydrogen ions accumulate in the ICF during states Hydrogen ions accumulate in the ICF during states of acidosis. Kof acidosis. K++ shifts out to maintain a balance of shifts out to maintain a balance of cations across the membrane.cations across the membrane.

Aldosterone, insulin, and catecholamines Aldosterone, insulin, and catecholamines influence serum potassium levelsinfluence serum potassium levels


HypokalemiaHypokalemia Potassium level <3.5 mEq/LPotassium level <3.5 mEq/L Potassium balance described by changes in Potassium balance described by changes in

plasma potassium levelsplasma potassium levels Causes: reduced potassium intake, increased Causes: reduced potassium intake, increased

potassium entry, and increased potassium potassium entry, and increased potassium lossloss

ManifestationsManifestations Membrane hyperpolarization causes a decrease in Membrane hyperpolarization causes a decrease in

neuromuscular excitability, skeletal muscle neuromuscular excitability, skeletal muscle weakness, smooth muscle atony, and cardiac weakness, smooth muscle atony, and cardiac dysrhythmias dysrhythmias


HyperkalemiaHyperkalemia Potassium level >5.5 mEq/LPotassium level >5.5 mEq/L Hyperkalemia is rare due to efficient renal Hyperkalemia is rare due to efficient renal

excretionexcretion Caused by increased intake, shift of KCaused by increased intake, shift of K++ from from

ICF, decreased renal excretion, insulin ICF, decreased renal excretion, insulin deficiency, or cell traumadeficiency, or cell trauma


HyperkalemiaHyperkalemia Mild attacksMild attacks

Hypopolarized membrane, causing neuromuscular Hypopolarized membrane, causing neuromuscular irritabilityirritability• Tingling of lips and fingers, restlessness, intestinal Tingling of lips and fingers, restlessness, intestinal

cramping, and diarrheacramping, and diarrhea

Severe attacksSevere attacks The cell is unable to repolarize, resulting in muscle The cell is unable to repolarize, resulting in muscle

weakness, loss of muscle tone, flaccid paralysis, weakness, loss of muscle tone, flaccid paralysis, cardiac arrestcardiac arrest


CalciumCalcium Most calcium is located in the bone as Most calcium is located in the bone as

hydroxyapatitehydroxyapatite Necessary for structure of bones and teeth, Necessary for structure of bones and teeth,

blood clotting, hormone secretion, and cell blood clotting, hormone secretion, and cell receptor functionreceptor function


PhosphatePhosphate

Like calcium, most phosphate (85%) is also located Like calcium, most phosphate (85%) is also located in the bonein the bone

Necessary for high-energy bonds located in Necessary for high-energy bonds located in creatine phosphate and ATP and acts as an anion creatine phosphate and ATP and acts as an anion bufferbuffer

Calcium and phosphate concentrations are rigidly Calcium and phosphate concentrations are rigidly controlledcontrolled CaCa++++ x HPO x HPO44

– –– – = K = K+ + (constant)(constant)

If concentration of one increases, that of the other If concentration of one increases, that of the other decreasesdecreases


Calcium and PhosphateCalcium and Phosphate

Regulated by three hormonesRegulated by three hormones Parathyroid hormone (PTH)Parathyroid hormone (PTH)

• Increases plasma calcium levels via bone reabsorptionIncreases plasma calcium levels via bone reabsorption

Vitamin DVitamin D• Fat-soluble steroid; increases calcium absorption from the GI Fat-soluble steroid; increases calcium absorption from the GI

tracttract

CalcitoninCalcitonin• Decreases plasma calcium levelsDecreases plasma calcium levels


Hypocalcemia and Hypocalcemia and HypercalcemiaHypercalcemia

HypocalcemiaHypocalcemia Decreases the block Decreases the block

of Naof Na++ into the cell into the cell Increased Increased

neuromuscular neuromuscular excitability excitability (partial (partial depolarization)depolarization)

Muscle crampsMuscle cramps

HypercalcemiaHypercalcemia Increases the block Increases the block

of Naof Na++ into the cell into the cell Decreased Decreased

neuromuscular neuromuscular excitabilityexcitability

Muscle weaknessMuscle weakness Increased bone Increased bone

fracturesfractures Kidney stonesKidney stones ConstipationConstipation


Hypophosphatemia and Hypophosphatemia and HyperphosphatemiaHyperphosphatemia

HypophosphatemiaHypophosphatemia Osteomalacia Osteomalacia

(soft bones)(soft bones) Muscle weaknessMuscle weakness Bleeding disorders Bleeding disorders

(platelet impairment)(platelet impairment) AnemiaAnemia Leukocyte alterationsLeukocyte alterations Antacids bind Antacids bind

phosphatephosphate

HyperphosphatemiaHyperphosphatemia See HypocalcemiaSee Hypocalcemia High phosphate High phosphate

levels are related to levels are related to the low calcium the low calcium levelslevels


MagnesiumMagnesium Intracellular cationIntracellular cation Plasma concentration is 1.8 to 2.4 mEq/LPlasma concentration is 1.8 to 2.4 mEq/L Acts as a co-factor in protein and nucleic acid Acts as a co-factor in protein and nucleic acid

synthesis reactionssynthesis reactions Required for ATPase activityRequired for ATPase activity Decreases acetylcholine release at the Decreases acetylcholine release at the

neuromuscular junctionneuromuscular junction


Hypomagnesemia and Hypomagnesemia and HypermagnesemiaHypermagnesemia

HypomagnesemiaHypomagnesemia Associated with Associated with

hypocalcemia and hypocalcemia and hypokalemiahypokalemia

Neuromuscular Neuromuscular irritabilityirritability

TetanyTetany ConvulsionsConvulsions Hyperactive reflexesHyperactive reflexes

HypermagnesemiaHypermagnesemia Skeletal muscle Skeletal muscle

depressiondepression Muscle weaknessMuscle weakness HypotensionHypotension Respiratory Respiratory

depressiondepression Lethargy, drowsinessLethargy, drowsiness BradycardiaBradycardia


pH: What Is It?pH: What Is It?

Negative logarithm of the HNegative logarithm of the H++ concentration concentration

Each number represents a factor of 10. If a Each number represents a factor of 10. If a solution moves from a pH of 7 to a pH of 6, the solution moves from a pH of 7 to a pH of 6, the HH+ + ions have increased 10-fold. ions have increased 10-fold.

Very acidicVery acidic Very alkalineVery alkaline

00 1414

NeutralNeutral

77Increasing H+ pH scale Decreasing H+Increasing H+ pH scale Decreasing H+


pHpH Inverse logarithm of the HInverse logarithm of the H++ concentration concentration HH++ high in number, pH is low (acidic) high in number, pH is low (acidic) HH++ low in number, pH is high (alkaline) low in number, pH is high (alkaline) Ranges from 0 to 14Ranges from 0 to 14 Each number represents a factor of 10. Each number represents a factor of 10.

If a solution moves from a pH of 6 to a pH of 5, the If a solution moves from a pH of 6 to a pH of 5, the HH++ has increased 10 times has increased 10 times


pHpH Acids are formed as end products of protein, Acids are formed as end products of protein,

carbohydrate, and fat metabolismcarbohydrate, and fat metabolism To maintain the body’s normal pH (7.35-7.45) To maintain the body’s normal pH (7.35-7.45)

the Hthe H++ must be neutralized or excreted must be neutralized or excreted Bones, lungs, and kidneys are major organs Bones, lungs, and kidneys are major organs

involved in regulation of acid-base balanceinvolved in regulation of acid-base balance


pHpH Body acids exist in two formsBody acids exist in two forms

VolatileVolatile• HH22COCO33 (can be eliminated as CO (can be eliminated as CO22 gas) gas)

NonvolatileNonvolatile• Sulfuric, phosphoric, and other organic acidsSulfuric, phosphoric, and other organic acids

• Eliminated by the renal tubules with the regulation of Eliminated by the renal tubules with the regulation of HCOHCO33

––


Buffering SystemsBuffering Systems Buffer systems exist as buffer pairs Buffer systems exist as buffer pairs

Associate and dissociate very quickly Associate and dissociate very quickly (instantaneous)(instantaneous)

Buffer changes occur in response to changes in Buffer changes occur in response to changes in acid-base statusacid-base status


Buffering SystemsBuffering Systems A buffer is a chemical that can bind excessive A buffer is a chemical that can bind excessive

HH++ or OH or OH–– without a significant change in pH without a significant change in pH A buffering pair consists of a weak acid and A buffering pair consists of a weak acid and

its conjugate base its conjugate base The most important plasma buffering systems The most important plasma buffering systems

are the carbonic acid–bicarbonate system are the carbonic acid–bicarbonate system and hemoglobinand hemoglobin


Carbonic Acid–Bicarbonate PairCarbonic Acid–Bicarbonate Pair Operates in the lung and the kidneyOperates in the lung and the kidney The greater the partial pressure of carbon The greater the partial pressure of carbon

dioxide, the more carbonic acid is formeddioxide, the more carbonic acid is formed At a pH of 7.4, the ratio of bicarbonate to carbonic At a pH of 7.4, the ratio of bicarbonate to carbonic

acid is 20:1acid is 20:1 Bicarbonate and carbonic acid can increase or Bicarbonate and carbonic acid can increase or

decrease, but the ratio must be maintaineddecrease, but the ratio must be maintained


Carbonic Acid–Bicarbonate PairCarbonic Acid–Bicarbonate Pair If amount of bicarbonate decreases, the pH If amount of bicarbonate decreases, the pH

decreases, causing a state of acidosisdecreases, causing a state of acidosis The pH can be returned to normal if the The pH can be returned to normal if the

amount of carbonic acid also decreasesamount of carbonic acid also decreases This type of pH adjustment is called compensationThis type of pH adjustment is called compensation

The respiratory system compensates by increasing or The respiratory system compensates by increasing or decreasing ventilationdecreasing ventilation

The renal system compensates by producing acidic The renal system compensates by producing acidic or alkaline urineor alkaline urine


Other Buffering SystemsOther Buffering Systems Protein bufferingProtein buffering

Proteins have negative charges, so they can serve Proteins have negative charges, so they can serve as buffers for Has buffers for H++

Renal bufferingRenal buffering Secretion of HSecretion of H++ in the urine and reabsorption of in the urine and reabsorption of

HCOHCO33––

Cellular ion exchangeCellular ion exchange Exchange of KExchange of K++ for H for H++ in acidosis and alkalosis in acidosis and alkalosis

(alters serum potassium)(alters serum potassium)


Acid-Base ImbalancesAcid-Base Imbalances Normal arterial blood pHNormal arterial blood pH

7.35 to 7.457.35 to 7.45 Obtained by arterial blood gas (ABG) samplingObtained by arterial blood gas (ABG) sampling

AcidosisAcidosis Systemic increase in HSystemic increase in H++ concentration concentration

AlkalosisAlkalosis Systemic decrease in HSystemic decrease in H++ concentration concentration


Acidosis and AlkalosisAcidosis and Alkalosis

Four categories of acid-base imbalances Four categories of acid-base imbalances Respiratory acidosis—elevation of pRespiratory acidosis—elevation of pCOCO2 2 due to due to

ventilation depressionventilation depression Respiratory alkalosis—depression of pRespiratory alkalosis—depression of pCOCO22 due to due to

alveolar hyperventilationalveolar hyperventilation Metabolic acidosis—depression of HCOMetabolic acidosis—depression of HCO33

–– or an or an

increase in noncarbonic acidsincrease in noncarbonic acids Metabolic alkalosis—elevation of HCOMetabolic alkalosis—elevation of HCO33

–– usually due to usually due to

an excessive loss of metabolic acidsan excessive loss of metabolic acids


CompensationCompensation RenalRenal

Alters bicarbonate and HAlters bicarbonate and H++ levels in response to levels in response to acidosis or alkalosisacidosis or alkalosis• Much slower responseMuch slower response

• Excretion and/or reabsorptionExcretion and/or reabsorption

RespiratoryRespiratory Alters COAlters CO2 2 retention or loss in response to retention or loss in response to

alkalosis or acidosis alkalosis or acidosis • Rapid responseRapid response

• Respiratory rate alterationsRespiratory rate alterations


CompensationCompensation When adjustments are made to bicarbonate When adjustments are made to bicarbonate

and carbonic acid in order to maintain the and carbonic acid in order to maintain the 20:1 ratio 20:1 ratio and and therefore maintain normal pHtherefore maintain normal pH The actual values for bicarbonate to carbonic acid The actual values for bicarbonate to carbonic acid

ratio are ratio are not normal but the normal ratio is not normal but the normal ratio is achievedachieved


CorrectionCorrection

Correction occurs when the values for BOTH Correction occurs when the values for BOTH components of the buffer pair (carbonic acid and components of the buffer pair (carbonic acid and bicarbonate) have also returned to bicarbonate) have also returned to normalnormal levels levels


Metabolic AcidosisMetabolic Acidosis


Anion GapAnion Gap Used cautiously to distinguish different types Used cautiously to distinguish different types

of metabolic acidosisof metabolic acidosis By rule, the concentration of anions (–) By rule, the concentration of anions (–)

should equal the concentration of cations (+). should equal the concentration of cations (+). Not all normal anions are routinely measured. Not all normal anions are routinely measured.

Normal anion gap = Normal anion gap = Na Na++ + K + K++ = Cl = Cl–– + HCO + HCO33

–– + 10 to 12 mEq/L + 10 to 12 mEq/L

(other misc. anions [the ones we don’t (other misc. anions [the ones we don’t measure]—phosphates, sulfates, organic measure]—phosphates, sulfates, organic acids, etc.)acids, etc.)


Anion GapAnion Gap Abnormal anion gap occurs due to an Abnormal anion gap occurs due to an

increased level of abnormal unmeasured increased level of abnormal unmeasured anion anion Examples: DKA—ketones, salicylate poisoning, Examples: DKA—ketones, salicylate poisoning,

lactic acidosis—increased lactic acid, renal failure, lactic acidosis—increased lactic acid, renal failure, etc.etc.

As these abnormal anions accumulate, the As these abnormal anions accumulate, the measured anions have to decrease to measured anions have to decrease to maintain electroneutralitymaintain electroneutrality


Metabolic AlkalosisMetabolic Alkalosis


Respiratory AcidosisRespiratory Acidosis


Respiratory AlkalosisRespiratory Alkalosis


SummarySummary

the cellular environment: fluids and electrolytes, acids and bases chapter 3 mosby items and derived...

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